Fair Value Measurements Fair Value Measurement (Details 2) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013		Sep. 30, 2013		Dec. 31, 2012	Sep. 30, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 820.1		$ 936.5		$ 566.9	$ 1,047.7
Notes Payable	3,461.9		3,509.0
Homebuilding [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, at Carrying Value	801.1		913.3
Restricted Cash and Cash Equivalents	81.1		77.8
Notes Payable	3,276.1		3,270.4
Homebuilding [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	801.1	[1]	913.3	[1]
Restricted Cash, Fair Value Disclosure	81.1	[1]	77.8	[1]
Homebuilding [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	801.1	[1]	913.3	[1]
Restricted Cash, Fair Value Disclosure	81.1	[1]	77.8	[1]
Financial Services [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, at Carrying Value	19.0		23.2
Financial Services [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	19.0	[1]	23.2	[1]
Financial Services [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure	185.8	[1]	238.6	[1]
Financial Services [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Securities Loaned or Sold under Agreements to Repurchase, Fair Value Disclosure	185.8	[1]	238.6	[1]
Cash and Cash Equivalents, Fair Value Disclosure	19.0	[1]	23.2	[1]
Senior Notes [Member] | Homebuilding [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable	2,783.5		2,783.3
Senior Notes [Member] | Homebuilding [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, Fair Value Disclosure	2,834.8	[2]	2,811.5	[2]
Senior Notes [Member] | Homebuilding [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, Fair Value Disclosure	2,834.8	[2]	2,811.5	[2]
2% convertible senior notes [Member] | Homebuilding [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable	487.0		478.7
2% convertible senior notes [Member] | Homebuilding [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, Fair Value Disclosure	859.7	[2]	762.4	[2]
2% convertible senior notes [Member] | Homebuilding [Member] | Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Notes Payable, Fair Value Disclosure	$ 859.7	[2]	$ 762.4	[2]

[1] The fair value approximates carrying value due to its short-term nature, short maturity or floating interest rate terms, as applicable.

[2] The fair value is determined based on quoted market prices of recent transactions of the notes, which is classified as Level 2 within the fair value hierarchy.